.header, .footer {
    height: 100px;
    background-color: antiquewhite;
    text-align: center;
    line-height: 100px;
}
.main {
    height: 350px;
    width: 1000px;
    margin: 0 auto;
}
.side {
    width: 300px;
    height: 350px;
    background-color: azure;
    float: right;
}
.content {
    width: 700px;
    height: 350px;
    background-color: beige;
    float: left;
}